1. Field of the Invention
This invention relates in general to sawmill equipment, and more particularly to an apparatus and method for positioning boards to be fed through board edging saws to expose maximum usable dimensioned lumber therefrom. In greater particularity, the present invention relates to an infeed table system for a board edge trimming device.
2. DESCRIPTION OF THE PRIOR ART
The boards handled by the infeed table are sawn cants. Cants are commonly described as planks of portions of logs after longitudinal ripsawing. They generally have flat top and bottom horizontal surfaces and unfinished and irregular longitudinal sides surfaces, called wane edges, which may still have bark. To produce dimensioned lumber, wane edges require to be eliminated. Conventionally an edging saw assembly will comprise at least two circular saws removing the wane edges of the board.
Numerous computer controlled systems have been developed to optimize the trimming of wane edges of boards to produce dimensioned lumber while minimizing waste. Optimization is obtained, for example, by using optical scanners which relay data on the specific morphology of a board to a computer which receives and analyses the data to control the board edge trimming process. The optical scanning method consists of transversely moving a board across light beams located at various points along the length of the board such that the light beam is interrupted and the restored as the board passes. The resultant measurement data is then fed to a computer which will compute a prescribed edging cut to maximize the production of useful dimensioned lumber. The computer will then control equipment which will effect such a preferred cut. Various examples of such systems are disclosed in the Sanglert U.S. Pat. No. 3,963,938 issued Jun. 15, 1976, in the Berry U.S. Pat. No. 4,086,496 issued Apr. 25, 1978, in the McGeehee U.S. Pat. No. 4,468,992 issued Sep. 4, 1984, and in the Wadell U.S. Pat. No. 4,471,823 issued Sep. 18, 1984.
With optical scanning systems, optimization of the edge trimming process is achieved in either of two ways. According to a first method, the edge trimming saws can be laterally adjustable relative to a constant edging path followed by every board as shown for example, by Sanglert U.S. Pat. No. 3,886,372. However, such methods require the replacement, at a great expense, of existing non-laterally adjustable board edging saw equipment with new computer controlled laterally adjustable board edging equipment. Consequently, such methods have failed to gain recognition and have failed in replacing conventional equipment.
In another method, optimization is achieved with conventional fixed position edge saws but the boards are precisely aligned on an preferred edging path determined by the computer based on the optical scanning data. This permits computer controlled cutting optimization systems to be used with existing fixed position board edging equipment (Horn et al U.S. Pat. No. 4,240,477). More particularly, Horn et al disclose a computer controlled alignment system using a movable mounting frame. Boards are laid on the mounting frame which is displaced, transversely to the edging path, to a final position which is computed to align the board with a preferred edging path and allow the board to be propelled by spiked feed rollers along the preferred edging path. The mounting frame slides on ball bearings on beams which are themselves bolted to the floor of the mill. Such systems have the inherent and severe drawback that they fail to be operable at the high processing speeds required in modern and efficient milling operations. To be more explicit, in the system disclosed by Horn et al, the mounting frame is moved by hydraulic cylinders. In addition, shock dampers are provided at each extremity of the range of movement of the mounting frame. In use, the mounting frame will slam against the hydraulic shock dampers and the momentum carried by the mounting frame will be transmitted to the support structure holding the hydraulic shock dampers and finally to the mill floor. If the system is accelerated, the slamming effect will in all probability increase to a point where the lumber resting on the mounting frame will skid on it and lose its alignment along the preferred edging path. This is especially true when slippery wet or frozen boards are being processed. More importantly, the entire assembly will become subjected to important structural shocks and will be prone to breakdowns.
Thus the need exists for board infeed optimization equipment which can smoothly and quickly position a board along a preferred edging path while being operable in conjunction with a conventional optical scanning system and conventional fixed woodworking equipment such as a fixed position edging device.